The production of stamped parts of high hardness from the high temperature forming process consists of heating a metal sheet (specific material) and then hardening of this material, by transforming the microstructure of the metallic material to conditions of higher hardness through quick cooling of the sheet already formed into its final shape inside the tool. This requires heating the plate from room temperature to the temperature called austenitizing temperature of the material, when its microstructure will have been transformed into austenite.
In this process, after heating, the work piece is conveyed automatically to a stamping mold located inside a press. The mold or tool, as is its technical denomination, has in its interior channels where a cooling liquid circulates to carry out the heat exchange with the assembly (tool+plate) and to promote its rapid cooling. Upon completion of cooling, the stamped part having a high hardness is then removed by an automated system and made available for the next operation, surface cleaning operation or laser cutting operation.
In the current state of the art, several types of specific equipment are used for heating, among them equipment that do heating by radiation, burning of fuel (commonly natural or LPG), electric heating (resistances) and heating through electric induction.
In equipment that use fuel heating, electric heating or mixed (electric+fuel) heating options of continuous furnaces, in which the part goes through a long path inside the furnace (over 10 meters in length), the part receives throughout the course the heat generated by fuel burning or by heating of electrical resistances, thus raising its temperature until it reaches the desired temperature at the furnace outlet. Usually these furnaces have zones with different and increasing temperatures, to which the plate is exposed along the path equaling its temperature with the temperature of each zone.
Stationary furnaces can also be used, where the part is deposited through a hatch into a chamber heated to high temperature, remaining there for a certain time until reaching the desired temperature when, when the hatch is opened and the piece is removed from inside the chamber.
In induction heating, the heat in the part is generated through an electric current by means of inducting an electric current on the plate by a coil (in which circulates a determined electric current) placed around the part to then generate an electric current in its inside and consequently its heating. This furnace may also be continuous or stationary, where in the continuous furnace the piece is led by a conveyor belt close to the heating coil, entering from one side at ambient temperature and leaving the other end at the desired temperature. In the stationary furnace the part is deposited in a chamber where the coils are located, and upon reaching the required temperature the piece is withdrawn from the interior.
In analyzing the existing equipment, it has been observed that in the case of continuous fuel and electric furnaces, as well as in continuous induction furnaces, there is a large consumption of space due to the length of the course required to be traveled in order to raise the temperature of the product. Thus, physical space occupied in the shed is large and impairs accommodation of other productive processes, storage, feasibility of logistical improvements, etc.
Another point observed is the heating rate, which affects the time required for heating and has a great impact on the productivity of a process. In the case of radiation heating, heating rates of approximately 6.5° C./sec can be achieved and in cases of induction heating, heating rates of 200° C./sec can be achieved.
As well as the previously mentioned shortcomings, energy consumption from inefficiencies in the heating process may generate a high cost of production for the company, and a more efficient process is always necessary so that costs can be reduced. In the case of radiation heating, the efficiency of a continuous furnace is approximately 26% and for induction heating this value lies between 40 and 60%.